System and Method for Low Power Signaling in a Wireless Local Area Network

ABSTRACT

A station, a method performed by a station and a corresponding method performed by an access point (AP) of a network to allow the station to operate a wireless local area network (WLAN) radio in a sleep state until the WLAN radio is ready to receive a beacon from the AP. The station includes a low power (LP) radio configured to receive a wake up signal from an AP of a network to which the station is connected. The station further includes a WLAN radio configured to operate in a sleep state until the WLAN radio receives an indication from the LP radio that the wakeup signal has been received, wherein WLAN radio is further configured to operate in a fully awake state after receipt of the indication to receive a beacon from the AP indicating a data transmission is pending for the station.

PRIORITY CLAIM/INCORPORATION BY REFERENCE

This application claims priority to U.S. Provisional Application61/928,914 entitled “System and Method for Low Power Signaling in aWireless Local Area Network,” filed on Jan. 17, 2014, the entirety ofwhich is incorporated herein by reference.

BACKGROUND INFORMATION

A wireless local area network (WLAN) may be used to exchange data fromone station to another station. The station that receives the data maybe configured using a duty cycle. The duty cycle may indicate a scheduleindicating a time duration in which the WLAN radio of the receivingstation is to be activated at select time periods to listen for beaconstransmitted from a network component such as an access point of theWLAN. The WLAN radio may be activated for a first predetermined timeperiod within the duty cycle and deactivated or placed to sleep (e.g.,hibernate) if no beacon is received in this time period. The WLAN radiomay sleep for a second predetermined time period after which the WLANradio is again activated for the first predetermined time period. Thismay repeat until a beacon is received by the WLAN radio while activated.The power required to activate and deactivate the WLAN radio isrelatively high and may be wasted, particularly when no beacon isreceived.

SUMMARY

In one exemplary embodiment, a station connected to a network performs amethod. The method includes receiving, by a low power (LP) radio of astation, a wake up signal from an access point (AP) of a network thestation is connected, the wake up signal configured to fully wake awireless local area network (WLAN) radio of the station and receiving,by the WLAN radio of the station, a beacon indicating a datatransmission is pending for the station.

In another exemplary embodiment, an access point (AP) of a networkperforms a method. The method includes determining at least one stationof the network to receive a data transmission, transmitting a wake upsignal to a low power (LP) radio of the at least one station, the wakeup signal configured to wake a wireless local area network (WLAN) radioof the at least one station and transmitting, by the AP, a beacon to theWLAN radio of the at least station, the beacon indicating the datatransmission is pending for the at least one station.

In a further exemplary embodiment, a station includes a low power (LP)radio and a wireless local area network (WLAN) radio. The LP radio isconfigured to receive a wake up signal from an access point (AP) of anetwork to which the station is connected. The WLAN radio is configuredto operate in a sleep state until the WLAN radio receives an indicationfrom the LP radio that the wakeup signal has been received, wherein WLANradio is further configured to operate in a fully awake state afterreceipt of the indication to receive a beacon from the AP indicating adata transmission is pending for the station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary network arrangement to transmit an indicationprior to transmitting a beacon indicating a subsequent datatransmission.

FIG. 2 shows an exemplary station configured to receive the indication,the beacon, and the subsequent data transmission.

FIG. 3 shows a first exemplary signaling diagram utilizing the wake upsignal.

FIG. 4 shows a second exemplary signaling diagram utilizing the wake upsignal.

FIG. 5 shows an exemplary block diagram of receiving the wake up signaland subsequent operations.

FIG. 6A shows an exemplary wake up signal format.

FIG. 6B shows an exemplary station indication signal format.

DETAILED DESCRIPTION

The exemplary embodiments may be further understood with reference tothe following description and the related appended drawings, whereinlike elements are provided with the same reference numerals. Theexemplary embodiments are related to systems and methods for low powersignaling in a WLAN. Specifically, an access point (AP) of the WLAN maytransmit an indication (e.g., a wake up signal) to a station scheduledto receive a data transmission prior to transmitting a beacon to thereceiving station. The receiving station may receive the indicationusing a first radio to activate a second radio such that the secondradio is configured to receive the beacon. The first radio may utilize alow power consumption for operation that is lower than the second radio.Therefore, the receiving station may conserve power by not using thehigher power second radio to continuously listen for the beacon. The lowpower signaling, the indication, the beacon, the AP of the WLAN, thereceiving station, the first and second radios, and the powerconservation will be described in further detail below.

Initially, it should be noted that the description below relates tousing the first and second radios as well as the wake up signal in aWLAN. However, the use of the WLAN is only exemplary. The exemplaryembodiments may also be used in various other network types including,for example, a peer-to-peer (P2P) network.

When a station is mobile, it is often restricted to using a portablepower supply, which is limited. Therefore, an important designconstraint for mobile stations is that a minimal amount of power be usedfor any given operation to allow the station to be used for a longerduration without being connected to a fixed power source. One particularapplication in for which lower power consumption is desirable is lowdata throughput and low duty cycle applications relating to datatransmissions. The station may be configured with a duty cycle thatindicates time intervals within a given time duration that a radio is tobe activated to listen for beacons. The beacon may represent, forexample, a management frame in the 802.11 specifications provided by theInstitute of Electrical Engineers (IEEE). Specifically, the beacon mayinclude information regarding a pending data transmission to be receivedby the station.

With a radio used in the 802.11 specifications, the power consumedduring the receiving functionality is relatively high. For example, in a5 GHz network, the power consumption could be 30% more than in a 2.4 GHznetwork. Those skilled in the art will understand that the powerconsumption to receive a data transmission is substantially similar tothe power consumption to look for a received signal. Accordingly, theradio utilizes a relatively large amount of power each time it isactivated and used to receive the beacon.

One manner of reducing this power consumption is maintaining a low dutycycle. For example, the radio consumes the large amount of power for asmaller amount of time, thereby reducing an overall power consumption ofthe station. For example, a duty cycle at 50% requires that the radio beactivated for half the time of the duration of the cycle. By decreasingthe duty cycle to a smaller amount such as 10%, the radio is activatedfor 40% less time within the duration of the cycle. Nevertheless, thelarge amount of power is still required each time the radio isactivated.

Furthermore, the low duty cycle only applies to when the radio isallowed to sleep during times it is not activated or being used.However, this is substantially impossible to achieve on a busy WLAN. Forexample, the radio must stay awake and activated to receive evenundesired packets. In another example, the WLAN may be congested to adegree that a beacon that is scheduled to be received according to aTarget Beacon Transmission Time (TBTT) known to the station is delayed.The station may therefore be required to maintain the radio in the fullpower activated state from the indicated time of the TBTT until thedelayed beacon is received.

In addition, the AP of the WLAN may have successfully indicated thatthere is a packet (i.e., data to be transmitted thereto as indicated inthe beacon) pending for the station. However, with a busy WLAN or forother reasons, the station must contend for the medium to send out apower save (PS)-Poll frame to solicit the frame since the radio has beenwoken from the sleep or power-saving mode. This may further worsen thepower consumption, as the radio must be maintained in the activatedstate until the PS-Poll frame is successfully transmitted to the AP.

The exemplary embodiments provide a mechanism to utilize low powersignaling as well as a mechanism to reduce a total time required for thehigh power consuming radio to be activated. That is, the high powerconsuming radio is allowed to sleep for an overall longer duration todecrease the power consumption. As used herein, the high power consumingradio will be referred to as a WLAN radio. The exemplary embodimentsutilize the WLAN radio and a further low power (LP) radio. The LP radiomay utilize a substantially smaller amount of power to operate than theWLAN radio. The LP radio may be configured to receive an indication orwake up signal from the AP of the WLAN. Accordingly, the AP of the WLANmay be configured to provide this wake up signal. The activated LP radiomay use a relatively low amount of power and receive the wake up signal,which is used to wake a sleeping WLAN radio (e.g., wake a PHY of thestation). In this manner, the WLAN radio is only woken when it is knownthat subsequent transmissions are destined for the station.Specifically, the WLAN radio is awake to receive a beacon that indicatesa subsequent data transmission of pending packets at the AP. As willalso be described in further detail below, the exemplary embodiments mayprovide further mechanisms that substantially prevent the station fromcontending for a medium as well as enable the LP radio to be used foruplink operations such as providing the PS-Poll frame.

FIG. 1 shows an exemplary network arrangement 100 to transmit anindication prior to transmitting a beacon indicating a subsequent datatransmission. The network arrangement 100 may include a network 105 andan AP 110 that is used by a plurality of stations 115-125 to connect tothe network. The network 105 may be, for example, a WLAN using a 802.11specification as defined by the IEEE. However, those skilled in the artwill understand that the network 105 may be any type of communicationsnetwork in which data is exchanged between at least one first electronicdevice and at least one second electronic device of the network itself.Accordingly, the network arrangement 100 may include further networkcomponents (not shown) such as servers, routers, network managementarrangements, network databases, etc.

The stations 115-125 may each be connected to the network 105 via the AP110. Specifically, the stations 115-125 may be associated with the AP110 using, for example, a handshake functionality. However, theexemplary embodiments also relate to and may be used for stations thatare non-AP stations. It should be noted that the number of the stations115-125 in the network arrangement 100 is only exemplary. Those skilledin the art will understand that any number of stations 115-125 may bepresent. It should also be noted that the network 105 may have anynumber of APs that may be used by the stations 115-125 to connect to thenetwork. In addition, there may be other types of devices that allownetwork access that are not APs. These other types of network accessdevices may also implement the functionality described herein for the AP110.

The AP 110 may be configured to transmit data indicated as having adestination to at least one of the stations 115-125. The data that is tobe transmitted by the AP 110 to one of the stations 115-125 may bereceived from the stations 115-125 or from the network 105. For example,the station 115 may transmit data destined for the station 125 via theAP 110. As will be described in further detail below, the AP 110 mayinitially transmit a wake up signal to the stations that are to receivethe data before transmitting a beacon that provides information as tothe transmission of the data. After the beacon has been transmitted, theAP 110 may then transmit the data to the stations.

FIG. 2 shows an exemplary station 200 configured to receive theindication, the beacon, and the subsequent data transmission.Specifically, the station 200 may represent an electronic device such asthe stations 115-125. More specifically, the station 200 may be anyportable device configured to exchange data with the network 105 such asa cellular phone, a smartphone, a tablet, a phablet, a laptop, etc. Thestation 200 may include a processor 205, a memory arrangement 210, adisplay device 215, an input/output (I/O) device 220, a WLAN radio 225,a LP radio 230, and other components 235.

The processor 205 may be configured to execute a plurality ofapplications of the station 200. For example, the applications mayinclude a text message application to receive a text from a furtherstation when connected to the network 105. In another example, theapplications may include a radio activation application that transmitssignals to the WLAN radio 225 to wake it (based upon signals from the LPradio 230) or to place the WLAN radio into a sleep state (e.g., basedupon expected transmission inactivity). It should be noted that theapplications being a program executed by the processor 205 is onlyexemplary. The applications may also be represented as a separateincorporated component of the station 200 or may be a modular componentcoupled to the station 200. It should also be noted that the use of theradio activation application is only exemplary. In another example, adirect signaling path may be established between the WLAN radio 225 andthe LP radio 230 in which the LP radio 230 performs the functionalitiesof the radio activation application. In another exemplary embodiment,the functionalities described for the radio activation application maybe implemented in a separate integrated circuit with or withoutfirmware.

The memory arrangement 210 may be a hardware component configured tostore data related to operations performed by the station 200. Forexample, the memory arrangement 210 may store the information receivedfrom the AP 110 relating to data transmissions. The display device 215may be a hardware component configured to show data to a user while I/Odevice 220 may be a hardware component configured to receive inputs fromthe user and output corresponding data. The other components 235 mayinclude a portable power supply (e.g., battery), a data acquisitiondevice, ports to electrically connect the station 200 to otherelectronic devices, an audio I/O device, etc.

The WLAN radio 225 may be a hardware component configured to transmitand/or receive data (e.g., a transceiver) with the network 105. Asdiscussed above, the WLAN radio 225 may be the high power consumingradio used in a 802.11 WLAN. Thus, when activated, the WLAN radio 225may consume, for example, 180 mW of power when the WLAN operates at 2.4GHz or 240 mW of power when the WLAN operates at 5 GHz. As will bedescribed in further detail below, the WLAN radio 225 may be in one oftwo states: awake/activated or asleep/deactivated. When awake, the WLANradio 225 may be configured to receive a beacon from the AP 110 as wellas data scheduled for transmission to the station 200.

Because the WLAN radio 225 operates using wireless signals, thesesignals are propagated using various frequencies. These frequencies maybe attained using, for example, a crystal oscillator. A crystaloscillator is an electronic oscillator circuit that uses the mechanicalresonance of a vibrating crystal of piezoelectric material (e.g., quartzcrystal) to create an electrical signal with a very precise frequency.As will be described in further detail below, the time required toactivate the crystals of the WLAN radio 225 may impact a manner in whichthe exemplary embodiments utilize the wake up signal. Specifically, thecrystals may require 3-5 ms to activate whereas other aspects of theWLAN radio 225 (e.g., PHY) may only require a fraction of that time. Forexample, for the WLAN radio 225 to be fully awake after the crystals areON, the PHY may be turned ON. The turning ON of the PHY requiresapproximately 500 μs to first be placed in a standby mode andapproximately another 50 μs to be placed ON. However, it should be notedthat the operation to place the PHY from standby to ON may be between25-100 μs.

It should be noted that the use of crystals in the WLAN radio 225 isonly exemplary. For example, non-crystal components may be used. Thecrystals may represent any oscillator that enables a selection of afrequency. Furthermore, the WLAN radio 225 may use other manners ofgenerating the signals at selected frequencies. For example,non-oscillator components may also be used. Therefore, the crystalsdescribed herein may represent any component of the WLAN radio 225 thatenables signals to be generated at a known frequency. Those skilled inthe art will understand that depending on these other manners, theexemplary embodiments may be modified to accommodate the timing issueswith using components in these other manners.

The LP radio 230 may be a hardware component configured to transmitand/or receive signals with the AP 110. Specifically, the LP radio 230may provide a specified data exchange functionality. As discussed above,the LP radio 230 may receive the wake up signal from the AP 110. In afirst example, the LP radio 230 may forward a corresponding signal tothe processor 205 such that the radio activation application may wakethe WLAN radio 225. For example, the processor may send an activationsignal to the WLAN radio 225 to activate the PHY to ON and the crystalsmay also be activated. In a second example, the activation signal forthe WLAN radio 225 may be generated by the LP radio 230 and thisactivation signal may be sent to the WLAN radio 225 via a direct pathwaybetween the LP radio 230 and the WLAN radio 225. Furthermore, after theactivation operation of the WLAN radio 225, the LP radio 230 may beconfigured to transmit a station indication signal that indicates to theAP 110 the current power state of the WLAN radio 225. That is, the lowpower signaling may also be used for subsequent signal transmissionsthat the AP 110 would normally require for the data transmission to beperformed. Accordingly, the WLAN radio 225 may not be required toperform this functionality.

As discussed above, the LP radio 230 may use a significantly smalleramount of power when activated as compared to the WLAN radio 225. Forexample, the LP radio 230 may use 400 μW of power when activated. Incomparison to the milli-Watts of power used by the WLAN 225, one skilledin the art will appreciate the amount of power conservation that may berealized. As such, it should be noted that the LP radio 230 may bemanufactured with components that are different or less complex than thecomponents used to manufacture the WLAN radio 225 but still configuredto perform the functionalities described herein.

It should be noted that the LP radio 230 having a lower powerconsumption by drawing 400 μW of power in comparison to the 180-240 mWof power drawn by the WLAN radio 225 is only exemplary. Specifically,this smaller amount of power used by the LP radio 230 relates to anyfurther radio that requires less power from being activated than theWLAN radio 225. That is, the overall amount of power used by the LPradio 230 to listen for a beacon is less than the overall amount ofpower used by the WLAN radio 225 to listen for the beacon.

According to the exemplary embodiments, the AP 110 may be configured toreceive or generate data to be transmitted to one or more of thestations 115, 120, 125. Prior to transmitting this data to the selectedstations 115-125, the AP 110 may notify the stations 115-125 that thereis an incoming data transmission. This notification provides informationto the selected stations 115-125 so that the WLAN radio 225 is to beawake and prepared to receive the data transmissions. As discussedabove, the WLAN radio 225 may be activated at select time intervalswithin a duty cycle to receive a beacon. However, according to theexemplary embodiments, the stations 115-125 may utilize the duty cycleto determine when the LP radio 230 is activated. Specifically, the LPradio 230 is activated for the duration of the duty cycle. It is notedthat the low power consumption of the LP radio 230 still results in anoverall decreased power usage than the standard waking/sleeping of theWLAN radio 225.

While the LP radio 230 is activated, it may listen for an incoming wakeup signal that is generated and transmitted by the AP 110. That is, partof the notification performed by the AP 110 includes an initial wake upsignal that is received by the LP radio 230. In a first example, the AP110 may generate the wake up signal for each of the stations 115-125that is scheduled for a subsequent beacon and data transmission. Forexample, if all the stations 115-125 are to receive a subsequent beaconand data transmission, the AP 110 may generate a respective wake upsignal for each of the stations 115-125. In another example, if thestations 115, 120 are to receive a subsequent beacon and datatransmission, the AP 110 may generate a respective wake up signal foronly these stations while no wake up signal is generated for the station125. In a second example, the AP 110 may also generate the wake upsignal in a broadcast manner for all the stations 115-125 to check thesubsequent beacon (e.g., instead of individual wakeup signals beinggenerated). In a third example, the AP 110 may group the stations andsend a wakeup signal in a group manner where one wakeup signal may betransmitted to all the stations in the group.

When the LP radio 230 of the select stations receive the wake up signal,the LP radio 230 may forward an activation signal to the WLAN radio 225(e.g., as described above, the activation signal may be directlyforwarded to the WLAN radio 225 or the LP radio may forward the wake upsignal to the processor 205 that generates the activation signal to sendthe WLAN radio 225). The activation signal may indicate that the WLANradio 225 is to wake from its sleeping state such as turning the PHY ONand possibly activating the crystals. As discussed above, the activationof the crystals in the WLAN radio 225 may affect the timing of thesignal transmissions with the AP 110. Accordingly, the exemplaryembodiments provide two mechanisms to use the wake up signal received bythe LP radio 230.

In a first exemplary embodiment, the stations 115-125 may be configuredto activate the crystal of the WLAN radio 225 for the duration of theduty cycle. That is, the LP radio 230 and the crystal of the WLAN radio225 may both be activated during the duration of the duty cycle.However, the PHY of the WLAN radio 225 may remain asleep. Morespecifically, the PHY of the WLAN radio 225 may be on standby (i.e., anintermediary setting between sleep and wake). By activating the crystalof the WLAN radio 225 for the duty cycle prior to a subsequent beacontransmission and placing the PHY on standby, a relatively fast wake upprocedure may be provided. Specifically, only the PHY of the WLAN radio225 is required to be turned ON since the crystal is already activated.As discussed above, the process to place the PHY from standby to ON mayneed less than 50 μs. Thus, the wake up signal from the AP 110 may betransmitted to the stations 115-125 about 50 μs before a beacon istransmitted. In this way, a sufficient amount of time is provided forthe stations 115-125 to be prepared to receive the beacon. Subsequently,a NOW signal may be transmitted from the AP 110 to the stations 115-125immediately prior to the beacon being transmitted. The NOW signal mayallow the stations 115-125 to save further power until an actual beacontransmission.

In a second exemplary embodiment, the stations 115-125 may be configuredfor the multi-stage wake up procedure. Specifically, the WLAN radio 225may be asleep in which the crystal is deactivated and the PHY is turnedOFF. Thus, to wake the WLAN radio 225, the crystal should be activated(using 3-5 ms) and the PHY should be placed on standby/ON (using 50-550μs). In view of this extended period of time that is required, the AP110 may transmit the wake up signal at least 4 ms before thetransmission of the beacon to allow sufficient time for the WLAN radio225 to be fully awake. After the wake up signal is transmitted, the AP110 may wait this predetermined time period and subsequently transmitthe NOW signal immediately prior to the beacon being transmitted. Itshould be noted the use of 4 ms is only exemplary and different waittimes may be used. However, it should also be noted that a delay greaterthan 4 ms may not be desired due to potential additional power loss.

Those skilled in the art will understand that the wake up signals maycause further stations that are not scheduled to receive a datatransmission to also wake. There may be a variety of reasons for such ascenario to arise. Thus, the exemplary embodiments provide a mechanismfor the wake up signal to be received only by the intended station.Specifically, the wake up signals are prevented from colliding withother network traffic. In a first example, the specifications definedunder 802.11 may be used. Specifically, the 802.11 protection frame maybe used prior to sending the wake up signal. In a second example, thewake up signals may be generated in such a way that it is impervious to802.11 traffic such as using a dedicated channel only for thetransmission of wake up signals.

It should be noted that other traffic may be on the air before thebeacon is transmitted. In view of this possibility of differenttransmissions occupying the medium being used for the wake up procedureand beacon transmission, the exemplary embodiments provide the timingfeature described above. For the first example, just enough time is setbetween the transmission of the wake up signal and the transmission ofthe beacon for the WLAN radio 225 to wake. The NOW signal mayimmediately be transmitted after transmitting the wake up signal with nogap therebetween. The NOW signal may initially provide the feature ofindicating that the beacon is being transmitted immediately after theNOW signal. The NOW signal may also provide a placeholder for the mediumsuch that the medium is still available for the beacon to betransmitted. For the second example, just enough time is set between thetransmission of the wake up signal and the transmission of the beaconfor the WLAN radio 225 to wake. However, there may be a gap between thetransmission of the wake up signal and the transmission of the NOWsignal. The NOW signal may therefore be used as described above to holdthe medium for the transmission of the beacon immediately following theNOW signal. The NOW signal may also be used to activate a medium accesscontrol (MAC) of the station to prepare to receive the beacon.

When viewing the transmission of data from the perspective of the AP110, the AP 110 may initially transmit a network packet. For example,the network packet may include a request for a medium for the subsequentdata transmissions. After the network packet is sent, the NetworkAllocation Vector (NAV) protection scheme may be used. As discussedabove, this may entail using the wake up signal that does not collidewith other network traffic. This wake up signal may be transmitted tothe select stations 115-125 that will also receive a beacon andsubsequent data transmission. The optional filler packet such as the NOWsignal may be transmitted immediately prior to the beacon beingtransmitted. Those skilled in the art will understand the use of anacknowledgement (ACK) signal when a signal has been transmitted.However, the exemplary embodiments may not utilize the ACK when the wakeup signal is transmitted. For example, the impervious nature of the wakeup signal may negate the need for the ACK.

The wake up signal may be formatted in a variety of manners. However,the wake up signal is designed to be transmitted by the AP 110 and to bereceived by the LP radio 230 of the selected stations. In an exemplaryembodiment, the wake up signal has a predetermined number of bits thatare relatively small. For example, only mandatory parameters may beincluded in the wake up signal. The parameters may include those relatedto addressing. Since a false positive may cause a redundant wake up, thewake up signal is not required to identify the transmitter and receiverof the radio fully. Thus, a reduced source address may be used (e.g.,last 6 bits of MAC address) and a reduced destination address may beused (e.g., last 6 bits of unicast or multicast or partial TIM bitmap).Optional parameters may also be included such as a frame type (e.g.,type and sub-type restricted to 6 bits) and an awake/sleep indicator(using 1 bit).

In a specific exemplary format and as illustrated in FIG. 6A, the wakeup signal 600 may include three fields. A first field may be a shortsource address. Examples of a short source address may be the partialsource MAC address or a hash of source MAC address. A second field maybe a beacon update. For example, whenever the AP 110 updates any beaconparameter, this field may be increased by one. The station may quicklydetermine whether a check is to be performed for a following beacon forthe updated parameter. In a third field may be a downlink dataindication. The downlink data indication may be an indication of whichstation or stations have pending downlink data (i.e., subsequent datatransmission after beacon). This may be a station AID bitmap (similar toTIM in the 802.11 specifications) or an address list. As shown in theFIG. 6A, the fields of the wake up signal may also have a specifiedorder so the stations will understand the data that is being received inthe wake up signal. However, it is not a requirement that the order bethe same as shown in FIG. 6A.

As discussed above, after the WLAN radio 225 has been awoken based onthe wake up signal received by the LP radio 230 and the WLAN radio 225has received the beacon, the LP radio 230 may again be used to indicatethe status of the WLAN radio 225 to the AP 110. That is, select ones ofthe stations 115-125 with the WLAN radio 225 awake may wish to indicateto the AP 110 the wake up status of the WLAN radio 225 and/or solicit apacket, namely the pending data transmission which prompted the wake upprocedure. Therefore, the low power signaling may be used in a reversedirection.

When conventional response signals are transmitted, the WLAN radio 225is used and must contend with other stations to send the PS-Poll frameor NULL or QoS NULL to the AP 110. This may waste a substantial amountof medium time for only a few bits of information (e.g., backoff, 802.11frame, etc.). The exemplary embodiments provide a mechanism thatutilizes the LP radio 230 to transmit the response.

Specifically, the station uses a station indication signal, which issubstantially similar to the wake up signal. The station indicationsignal informs the AP 110 about the current status of the WLAN 125(e.g., power mode) and whether it has packets to transmit/receive. Thestation indication signal may be sent as a response to an optional polltransmitted by the AP 110 immediately after the beacon is transmitted.However, even with no poll, the LP radio 230 may be used to transmit thestation indication signal. It should be noted that the poll may betransmitted as a separate signal, may be implicit, or may be includedwith the beacon. In this manner, the low power signaling may again beused to transmit the station indication signal from the stations 115-125to the AP 110. The station indication signal will not collide with othernetwork traffic. It should be noted that it may be assumed that multipleindication frames may be sent concurrently such as by utilizingdifferent tones.

The station indication signal may also be formatted in a variety ofmanners substantially similar to the wake up signal. In a specificexemplary format and as illustrated in FIG. 6B, the station indicationsignal 650 may include three fields. A first field may be a short sourceaddress. This field may be substantially similar to the short sourceaddress of the wake up signal but may also be a partial AID or similar(non-strictly) unique identifier. A second field may be a shortdestination address. For example, the short destination address may be apartial destination MAC address, a hash of destination MAC address, orsimilar (non-strictly) unique identifier. A third field may be a powermode. The power mode may be an indication of the state of the WLAN radio225. For example, a power mode (PM) of 0 may indicate that the WLANradio 225 is awake; a PM of 1 may indicate that the WLAN radio 225 isasleep; a PM of 3 may indicate that the WLAN radio 225 is asleep but maybe woken up with a wake up signal trigger; etc.

FIG. 3 shows a first exemplary signaling diagram 300 utilizing the wakeup signal. Specifically, the signaling diagram 300 relates to the firstexemplary embodiment described above in which the crystal is activatedfor the duration of the duty cycle. The signaling diagram 300 willdescribe an exchange of signals between the AP 110 and the station 115.However, it should be clear that the same type of signaling may occurbetween the AP and the other stations 120 and 125. An initial step maybe to determine a beginning of the duty cycle. When the duty cyclestarts, the crystal of the WLAN radio 225 may be activated 305. The LPradio 230 may also be activated at the beginning of the duty cycle.

The AP 110 may determine that the station 115 is to receive a beacon anda subsequent data transmission. Thus, the AP 110 generates a wake upsignal 310 for the station 115. The wake up signal 310 is transmittedfrom the AP 110 to the LP radio 130 of the station 115. It should benoted that the wake up signal transmitted to the LP radio 230 may betransmitted in the same band as the signals that will be transmitted tothe WLAN radio 225 or may also be transmitted on any other band that isavailable for transmission. That is, the band on which the wake upsignal is transmitted is not important to the exemplary embodiments,merely that the wake up signal is transmitted and received. The LP radio230 forwards an activation signal 315 to the WLAN radio 225 such thatthe PHY of the WLAN radio 225 is turned ON 320. As described above, theactivation signal 315 may be sent directly from the LP radio 230 to theWLAN radio 225 or via the processor 225. The AP 110 may also activate atimer 325 upon transmitting the wake up signal 310. In the firstexemplary embodiment, this timer 325 may be set to 50 μs. The durationof the timer is set based upon a time required for the WLAN radio 125 tobe fully awake.

The expiration of the timer 325 indicates when the beacon is to betransmitted by the AP 110. Immediately before the timer 325 expires, theAP 110 may transmit the NOW signal 330 to the WLAN radio 225 which isnow awake. The receipt of the NOW signal 330 may also cause the station115 to activate the MAC 340 to prepare to receive the beacon. The NOWsignal 330 may occupy the medium used for the beacon transmission. Thus,when the timer 325 expires, the beacon 335 is transmitted over the knownmedium without other network traffic commandeering this medium.

After the beacon 335 is transmitted, the AP 110 may optionally transmita poll 345 for a response. The WLAN radio 225 may determine its status350 and provide this information via a status signal 355 to the LP radio230. The LP radio 230 may transmit the station indication signal 360(e.g., PS-Poll frame) back to the AP 110. As described above, the statusindication signal 360 may provide information concerning the station 115to the AP 110, e.g., the activation state of the WLAN radio 225.

FIG. 4 shows a second exemplary signaling diagram 400 utilizing the wakeup signal. Specifically, the signaling diagram 400 relates to the secondexemplary embodiment described above in which the multi-stage wake upprocedure is used and the crystal is activated after receiving the wakeup signal. The signaling diagram 400 will also be used to describesignals that are exchanged between the AP 110 and the station 115.Again, an initial step may be to determine a beginning of the dutycycle. When the duty cycle starts, the LP radio 230 may be activated.

Again, the AP 110 may determine that the station 115 is to receive abeacon and a subsequent data transmission. Thus, the AP 110 generates awake up signal 405 for the station 115. The wake up signal 405 istransmitted from the AP 110 to the LP radio 230 of the station 115. TheLP radio 230 forwards a activation signal 410 to the WLAN radio 225 suchthat the crystal is activated 415 and the PHY of the WLAN radio 125 isturned ON 420. Upon transmitting the wake up signal 405, the AP 110 mayactivate a timer 425. In the second exemplary embodiment, this timer 425may be set to 4 ms. Again, the duration of the timer 425 is set basedupon a time required for the WLAN radio 125 to be fully awake. Since, inthis embodiment, the activation signal 410 signals that the crystalshould be turned on, the time 425 is set to a longer duration than thetime 325 of the previous embodiment where the crystal was turned on atthe beginning of the duty cycle.

Subsequent steps including the transmission of the NOW signal 430 to theWLAN radio 225, the activation 440 of the MAC of the station 115, thetransmission of the beacon 435 to the WLAN radio 225, the optionaltransmission of the poll 445, the status determination 450, the statussignal 455 and the station indication signal 460 may be substantiallysimilar to the first exemplary embodiment described above with regard tothe signaling diagram 300.

FIG. 5 shows an exemplary block diagram 500 of an exemplary stationreceiving the wake up signal and subsequent operations. Specifically,the block diagram 500 illustrates components of the LP radio 230 and theWLAN radio 225 used in the wake up procedure including the use of thewake up signal. As illustrated, the top half of the block diagram 500may represent the LP radio 230 while the bottom half of the blockdiagram 500 may represent the WLAN radio 225. Since both the WLAN radio225 and the LP radio 230 are part of a common station, the MAC addressdisposed between the WLAN radio 225 and the LP radio 230 may represent ahigh level layer.

Initially, as discussed above, the LP radio 230 may receive a wake upsignal using its antenna. The wake up signal may be processed using avariety of components whose functionality is known to those skilled inthe art. For example, the LP radio 130 may include an amplifier module,a mixer, a filter, an analog/digital module, an AGC module, an offsetestimation module, a channel estimation module, an equalizer, a decoder,and an identifier. The identifier may generate the activation signal.The activation signal include power on signals that are forwarded tosub-components of the WLAN radio 125 such as the analog RF portion, thedigital front end portion, and the digital block portion.

With the power on signals being received, each portion may be activated.Specifically, the crystals may be activated and the PHY may be turnedon. The WLAN radio 125 may also include a variety of components whosefunctionality is known to those skilled in the art. For example, theWLAN radio 125 may include a RF module, a filter, an analog/digitalmodule, a AGC module, a CRS module, an offset estimation module, achannel estimation module, a FFT module, a demodulator, a decoder, and aMAC module. Thus, when the beacon is received by the WLAN radio 125using its antenna, the beacon may be processed.

The exemplary embodiments provide a system and method for a low powersignaling that conserves power. The stations may include a first radio(i.e., WLAN radio) used for receiving a beacon and a subsequent datatransmission indicated in the beacon. The stations may further include asecond radio (i.e., LP radio) used for receiving a wake up signal thatwakes the WLAN radio from a sleep state. Using the LP radio that doesnot use a high power, the station may conserve a limited power supply bykeeping the high power using WLAN radio asleep for longer periods oftime and only activating the WLAN radio for pending packets to bereceived.

It should be noted that the wake up PHY design may relate to minimizinga receiving power and using a transmission power no larger than other802.11 PHY parameters. That is, the receiving bandwidth, the noisefigure, the dynamic range, and LO phase noise requirements are reduced.Since the wake up signal does not include a data payload, the LP radiomay be configured with low power consuming components. The wake upsignal may have a sensitivity matching a lowest data rate (e.g., 6Mbps). Furthermore, false alarms are minimized from AWGN and 802.11traffic. It should also be noted that parameters of 2 or 4-FSK may bewith a simple block code. Furthermore, the frequency of operation forthe wake up signal may be on an existing channel or a new narrowbandwidth channel (e.g., between channel 6 and 11). In addition,simultaneous wake up signal transmissions may be performed usingdifferent tones for each wake up signal with some repetition and/or usea spread spectrum.

Those skilled in the art will understand that the above-describedexemplary embodiments may be implemented in any suitable software orhardware configuration or combination thereof. An exemplary hardwareplatform for implementing the exemplary embodiments may include, forexample, an Intel x86 based platform with compatible operating system, aMac platform, MAC OS, iOS, Android OS, etc. In a further example, theexemplary embodiments of the above described method may be embodied as aprogram containing lines of code stored on a non-transitory computerreadable storage medium that, when compiled, may be executed on aprocessor or microprocessor.

It will be apparent to those skilled in the art that variousmodifications may be made in the present invention, without departingfrom the spirit or the scope of the invention. Thus, it is intended thatthe present invention cover modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalent.

What is claimed is:
 1. A method, comprising: receiving, by a low power(LP) radio of a station, a wake up signal from an access point (AP) of anetwork the station is connected, the wake up signal configured to fullywake a wireless local area network (WLAN) radio of the station; andreceiving, by the WLAN radio of the station, a beacon indicating a datatransmission is pending for the station.
 2. The method of claim 1,further comprising: activating, by the station, a crystal of the WLANradio and the LP radio at a beginning of a duty cycle, wherein the wakeup signal turns a physical layer (PHY) of the station on.
 3. The methodof claim 2, wherein the beacon is received at substantially 50 μs afterthe wake up signal is received, wherein the 50 μs corresponds to anapproximate time for the PHY of the station to turn on.
 4. The method ofclaim 1, further comprising: activating, by the station, the LP radio ata beginning of a duty cycle, wherein the wake up signal turns a crystalof the WLAN radio and a PHY of the station on.
 5. The method of claim 4,wherein the beacon is received between 3 to 5 ms after the wake upsignal is received, wherein the 3 to 5 ms corresponds to an approximatetime for the crystal and the PHY of the station to turn on.
 6. Themethod of claim 1, further comprising: sending, by the LP radio, anactivation signal based on the wakeup signal directly to the WLAN radiothat causes the WLAN radio to fully awake.
 7. The method of claim 1,further comprising: sending, by the LP radio, an indication of thereceipt of the wakeup signal to a processor of the station; and sending,by the processor, an activation signal to the WLAN radio that causes theWLAN radio to fully awake.
 8. The method of claim 1, further comprising:receiving, by the LP radio of the station, a poll from the AP requestinga power mode status of the WLAN radio; determining, by the station, thepower mode status of the WLAN radio; and transmitting, by the LP radioof the station, a station indication signal to the AP, the stationindication signal indicating the power mode status.
 9. The method ofclaim 1, further comprising: receiving, prior to receiving the beacon, aNOW signal, wherein the NOW signal wakes up a medium access control(MAC) module of the station.
 10. A method, comprising: determining, byan access point (AP) of a network, at least one station of the networkto receive a data transmission; transmitting, by the AP, a wake upsignal to a low power (LP) radio of the at least one station, the wakeup signal configured to wake a wireless local area network (WLAN) radioof the at least one station; and transmitting, by the AP, a beacon tothe WLAN radio of the at least station, the beacon indicating the datatransmission is pending for the at least one station.
 11. The method ofclaim 10, further comprising: setting a timer when the wakeup signal istransmitted.
 12. The method of claim 11, wherein the beacon istransmitted a predetermined time period after the wake up signal istransmitted, the predetermined time period being measured by the timer.13. The method of claim 12, wherein the predetermined time period is oneof between 25 to 100 μs when a crystal of the WLAN radio is alreadyactivated and between 3 to 5 ms when the crystal of the WLAN radio isdeactivated.
 14. The method of claim 10, further comprising:transmitting, by the AP, a poll to the LP radio of the at least onestation, the poll requesting a power mode status of the WLAN radio ofthe at least one station; and receiving, by the AP, a station indicationsignal from the LP radio of the at least one station, the stationindication signal indicating the power mode status.
 15. The method ofclaim 11, further comprising: transmitting, by the AP, a NOW signalafter the timer has been set and before transmitting the beacon, whereinthe NOW signal occupies a medium to be used to transmit the beacon, andwherein the NOW signal wakes up a medium access control (MAC) module ofthe at least one station.
 16. A station, comprising: a low power (LP)radio configured to receive a wake up signal from an access point (AP)of a network to which the station is connected; and a wireless localarea network (WLAN) radio configured to operate in a sleep state untilthe WLAN radio receives an indication from the LP radio that the wakeupsignal has been received, wherein WLAN radio is further configured tooperate in a fully awake state after receipt of the indication toreceive a beacon from the AP indicating a data transmission is pendingfor the station.
 17. The station of claim 16, wherein the WLAN radioincludes a crystal and a physical layer (PHY), wherein the sleep stateincludes the crystal being powered on and the PHY being in an off orstandby state and the fully awake state includes the crystal beingpowered on and the PHY being powered on.
 18. The station of claim 16,wherein the WLAN radio includes a crystal and a physical layer (PHY),wherein the sleep state includes the crystal being powered off and thePHY being in an off or standby state and the fully awake state includesthe crystal being powered on and the PHY being powered on.
 19. Thestation of claim 16, wherein the LP radio is configured to operate in asleep state until activated by a start of a duty cycle.
 20. The stationof claim 16, further comprising: a processor configured to receive afurther indication from the LP radio that the wakeup signal was receivedand provide the indication to the WLAN radio.